AWS Archives

How to use the power of CloudFormation custom resources for great good

AWS, CloudFormation, Lambda, Programming, Serverless

Disclaimer: if you’re new to CloudFormation custom resources, then I recommend you start by reading this excellent post by Alex Debrie first. Custom resources bring a whole new dimension to CloudFormation and enable some fascinating use cases. For example: provision DataDog dashboards as part of your CloudFormation stack run a load test every time you …

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A simple event-sourcing example with snapshots using Lambda and DynamoDB

AWS, DynamoDB, Lambda, Programming, Serverless

Recently, I have been helping a client implement an event-sourced system. In the process, I put together a very simple demo app to illustrate how one could build such a system using Lambda and DynamoDB. The source code is available on GitHub here. Before you go ahead and read all about the demo app, I …

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How to do blue-green deployment for Step Functions

AWS, Lambda, Programming, Serverless, Step Functions

A client asked me the other day: “What happens to the running executions when I update a state machine?” Sadly, the answer is likely that existing executions would break if you have changed the input/output of the Lambda functions they call. The solution is to use specific versions or aliases of the functions instead. But …

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How to make serverless framework boilerplates customizable

AWS, Lambda, Programming, Serverless

The Serverless framework lets you reference external JSON, YML and JS files using the syntax ${file:(fileName):propertyName}. However, you can’t customize these external config files with runtime arguments. A reader asked me: “I have this boilerplate that is repeated many times in my serverless.yml, how do I reuse the boilerplate but override only specific fields?” It’s …

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Serverless Step Functions: no more leaky abstractions

AWS, Lambda, Programming, Serverless, Step Functions

I have some exciting news to share with you about the Serverless Step Functions plugin. One of the main pain points of using the plugin was that you needed to use fully-formed ARNs. We addressed this in v1.18.0 by supporting CloudFormation intrinsic functions Fn:GetAtt and Ref. This makes it possible for you to reference a …

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Introducing a better way to record custom metrics

AWS, CloudWatch, Lambda, Programming, Serverless

Many clients have asked me “how do I record custom metrics from Lambda?”. Generally speaking, you can either: Publish custom metrics synchronously – e.g. send them at the end of an invocation. Publish custom metrics asynchronously by writing them to stdout first and then extracting them from CloudWatch Logs. Problems with sending custom metrics synchronously …

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How to connect SNS to Kinesis for cross-account delivery via API Gateway

API Gateway, AWS, Kinesis, Lambda, Programming, Serverless, SNS

At DAZN (where I no longer work), the teams work with a number of third-party providers. They often have to synchronize data between different AWS accounts. SNS to SQS is the primary mechanism for these cross-account deliveries because: it was an established pattern within the organization DAZN engineers and third-party engineers are both familiar with …

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AWS Lambda: how to share code between functions in a monorepo

AWS, Lambda, Programming, Serverless

A while back, a client asked me “how can I share business logic between services in a Node.js monorepo?”. The TL;DR of it is: Encapsulate the shared business logic into modules, and put them in a separate folder. In the Lambda handler functions, reference the shared modules using relative paths. Use webpack to resolve and …

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Step Functions as an ad-hoc scheduling mechanism

AWS, Design Patterns, Lambda, Programming, Serverless, Step Functions

We previously discussed how you can implement an ad-hoc scheduling system using DynamoDB TTL as well as CloudWatch Events. And now, let’s see how you can implement the same system using AWS Step Functions and the pros and cons of this approach. As before, we will assess this approach using the following criteria: Precision: how …

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AWS Lambda: how to detect and stop accidental infinite recursions

AWS, Lambda, Programming, Serverless

Lambda makes it easy to build event-driven architectures. Each function only needs to look after its own responsibilities. We chain them together through APIs, queues, streams, and other event sources. It’s a good way to build complex systems out of simple components. We need only managed services, and we only pay for them when we …

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